The present invention relates generally to a fluid dispensing system with a device for controlling the flow of fluids through a plurality of valves, and more particularly to a shaft-mounted cam that through a combination of translational and rotational motion can sequentially open or close one or more valves to precisely control the ratio of fluids added to a fluid mixture.
The use of valves and valve actuators to control the flow of gases and liquids in a fluid combining process or system is well known in the art. One area where precise actuation and control of the valves is critical is in chemical processes, where a large number of valves are employed, often in an extensive array of piping, conduit, ducting or related fluid carrying and containing equipment. The attendant level of monitoring and process control necessary to ensure that these larger, more complex valving systems are performing their intended tasks has rendered manual control of such systems difficult. In response, automated valve control was developed, and with the advent of computer-controlled systems, even more sophisticated ways to control and monitor any given chemical process have become commonplace. While the more precise, predictable control over valve closure and opening associated with automated devices has enabled improved system functionality, it has come with system cost, weight and complexity burdens.
Many of today""s modern chemical processes, including oil or petroleum refining, food and drug manufacturing and electric generation, rely extensively on the complex interconnection of pumps, piping and valves to effect a particular chemical conversion or mixture. One of the more frequently used forms of chemical processing involves the use of a fluid dispensing system, wherein a single fluid transport conduit permits multiple fluids to be selectively injected into a main stream to create a final mixed product for dispensing. However, there are situations in which fluid dispensing systems, although potentially beneficial, have not found application. One example is the preparation of etchants for metals in the metallurgical laboratory. They are usually prepared in small quantities (typically 100 ml or less), and owing to their reactivity with metals are corrosive and hazardous by nature. Typically, these etchants are recipes comprising a mixture of constituents formulated to react with a given metal. As such, precise control over the ratios to ensure a quality etchant mixture is necessary. While such precise control with prior art systems embodying fluid dispensing features is possible, their reliance on multiple dedicated pumps or redundant valve and actuator engaging configurations results in complex, expensive systems that require that each actuator must be equipped with numerous dedicated devices in order to control multiple valves.
Another especially acute problem involves the precise control of minute quantities of fluids. When small quantities of injectants are being mixed, such as with medicament samples, acid etchants and related chemical reagents, the lack of a simplistic fluid dispensing system, which can meter precise amounts of the desired fluids reliably, affordably and safely is a hindrance to the creation of application-specific fluids. In response to ever-increasing demands that end product mixtures be of extremely high quality, with minimal contamination, waste and risk of exposure of personnel or the environment to hazardous substances, existing systems have added backup and redundant componentry, exacerbating system cost and complexity. Depending on the size of the fluid transport conduit in a fluid dispensing system, the driver fluid in the conduit""s main stream could be either a conventional liquid (most notably water) carrier or an immiscible gas (most notably air) being drawn into the main stream through a supply valve. With a liquid-based driver system, a xe2x80x9cpusherxe2x80x9d fluid is used to move the injectant through the main stream of the conduit and into the dispensing unit. By using an xe2x80x9call liquidxe2x80x9d approach (i.e.: liquid pusher and liquid injectant), the potential for an extremely accurate final mixture exists, due in part to the incompressibility of the liquids. However, the present inventors have discovered that the size of the conduit effects the mixing process. If the conduit is too large, the discrete volume of fluid in the conduit tended to collapse and mix with the pusher fluid. Likewise, if the size of the conduit is too small (as can be the case when small quantities of injectant are used), friction effects can dominate, resulting in slow dispensing speeds and higher power requirements.
In metallurgical laboratories, metallurgists and metallurgical technicians routinely prepare etchants, mixtures of acids, solvents, and salts, which are used to etch metallographic samples, thus revealing microstructure and other features. The preparation of etchants, as it is currently practiced in the metallurgical lab, entails: the transfer of acids and solvents from the bottles in which they are supplied to smaller containers to facilitate handling; the measurement of volumetric quantities of these acids and solvents using graduated cylinders; and the mixing of the same in a container along with mass quantities of salts, if required. The handling and measurement activities are time consuming and entail significant risk to both personnel and the environment. Alternatively, some laboratories transfer acids and solvents from the containers in which they were purchased into an individual dispenser for each reagent, or insert a bottle top dispenser into each bottle in which a reagent is purchased. After the etching operation is completed, the etchant must be neutralized prior to disposal. Many laboratories perform the pH neutralization procedure with sodium hydroxide pellets. Because sodium hydroxide is highly reactive in acid, as are related acid neutralizers, it must be added slowly to minimize foaming and spatter. Personnel performing this operation check the neutralization process frequently using litmus paper to determine the pH of the solution. This can be tedious, time-consuming, and potentially dangerous to personnel, adjacent laboratory equipment and the ambient environment. In addition, it is frequently the case that too much neutralizer is added, thus necessitating the addition of more acid in an ad hoc process to ensure that an acceptable pH (typically in the range of 6 to 8) is reached prior to disposal. Not only does the prolonged exposure due to this back-and-forth process present additional risks to personnel, equipment and the environment, but it generates additional quantities of waste product as well.
Other applications for a fluid dispensing system capable of handling acids and solvents exist outside of the metallurgical laboratory. One example is compositional analysis of metals in the chemical laboratory using a technique known as inductively coupled plasma. Prior to analysis, the metal to be analyzed must be placed in liquid solution. To accomplish this, chemists dissolve the metallic sample in mixtures of acids and solvents similar to etchants. In the chemical laboratory, the preparation, neutralization and disposal of these solutions of acids and solvents proceeds in much the same way as it does in the metallurgical laboratory. Similarly, in other contexts, examples of commercially available systems exist in which a peristaltic pump is devoted to each liquid to be dispensed. Such systems may be combined with valve manifolds to redirect liquids to a plurality of locations. Valves in such manifolds are generally activated individually using electromechanical devices such as solenoids. Other commercially available systems use multiple screw driven syringes or multiple syringe pumps to dispense a multiplicity of liquids. In any event, exposure to harsh chemicals can present safety and operability risks that typically require additional costs associated with redundant, protective system componentry.
Accordingly, there exists a need for a fluid dispensing system that can offer greater simplicity, improved safety to using personnel, improved conservation of constituent fluids, and greater speed of fluid mixture preparation.
This need is met by the present invention by providing a simple, reliable means for controlling the opening and closing of multiple fluid insertion valves arranged in a common valve manifold without having to rely on the use of complicated, redundant actuators. The current invention preferably employs a cam which can be translated by means of a lead screw across a linear array of valves and rotated to actuate a given valve when located in juxtaposition to that valve. By placing a single pump upstream of the valve manifold and a dispensing nozzle downstream, the multiplicity of pumps can be eliminated. The inventors of the present invention have further recognized that their approach increases throughput of the dispensed final product while avoiding the complexity and redundancy of larger, heavily-arrayed fluid transport conduit systems. One of the chief attributes to the system of the present invention is that by using a single cam on a single shaft as a valve actuator engaging member, thus resulting in a single translation member and a single rotation member, the device is inherently simple and compact. Further system simplicity is ensured by the use of one or more conventional motors to move the cam, such as a stepper motor, servomotor or rotary solenoid. Alternatively, the use of multiple pumps of different sizes could be employed to achieve high volumetric accuracy when small amounts of reagent are to be injected into large amounts of solution. In this case pumps with different capacities may be plumbed either in parallel or in series in such a way that the smaller pump provides greater accuracy during aspiration where as the larger pump provides greater capacity during aspiration and greater speed during dispensing.
In accordance with one embodiment of the present invention, a fluid dispensing system (also known as an injectant dispensing system) is disclosed. It includes at least one pump for metering precise quantities of fluid to be dispensed; one or more fluid injection lines for transporting a fluid to be dispensed, and one or more valves with valve actuators, each of the valves disposed in one of the fluid injection lines, wherein the fluid injection lines can be in fluid communication with fluid dispensing containers at one end, and with a fluid transport conduit at the other. The fluid transport conduit is also in fluid communication with the pump. Each of the valves can control the flow of a quantity of fluid through one of the fluid injection lines. At least one valve actuator engaging member is coupled to each of the valve actuators so that, based on a control signal, each actuator engaging member can force a respective actuator on the valve to open or close the valve in response to the control signal. Furthermore, a pusher fluid is selectively introduced into the fluid transport conduit to force the flow of a fluid to be dispensed through the fluid transport conduit. In the present context, a pusher fluid is one used as a carrier, such that it moves the injectant fluid through the fluid transport conduit and into the pump. The choice of a particular pusher fluid can effect the way many of the system elements are interconnected. Specifically, the size of the fluid transport conduit, pump size and type can be tailored to the dispensing of small quantities of fluids to minimize or prevent fluid intermixing and residual droplet formation. In addition, the present inventors discovered that if the pusher fluid is a liquid, an optional filter device can be disposed in the pusher fluid injection line to not only reduce contaminant presence but also provide damping for flow stability. A flow detection system is disposed adjacent the fluid injection lines, and includes at least one detector and a controller in electrical communication with the detector, valves and pump such that upon detection and comparison of a flow variation, the controller sends signals to at least one of the pump or valves to control the flow of fluid. This system is especially well-suited to the use of acids, solvents and acid neutralizers.
Optionally, to meet the need of ensuring that the highly accurate approach of using a liquid pusher with a small bore conduit could be replicated without the aforementioned speed and power drawbacks, the present invention further may include an immiscible gas as the pusher in small conduit lines (such lines being commonly associated with the use of acid reagents for etchant solutions). Thus, by using a gaseous pusher fluid for small mixture quantities, where an appropriate amount of conduit is placed between the pump and the fluid injection valves in the absence of a liquid pusher, the aspiration of the fluid could be accurately metered, resulting in precise mixtures to be dispensed. Advantages of this approach include the use of a smaller, more simplistic fluid transport conduit, as well as reducing the need to dilute or mix the fluid with a water-based main stream carrier. As another option, the fluid dispensing system can include a capping mechanism adapted to be disposed in the container apertures, thus acting as a stopper to prevent unintended release of fluids from the container. Furthermore, the capping mechanism permits the flow of fluid to and from the container under normal operating conditions by being operatively responsive to pressure differentials arising out of putting fluid into and taking fluid out of the container. The capping mechanism, which is operatively responsive to a pressure differential across the aperture in each of the containers, can include the following features: a generally cylindrical body; at least one threaded groove disposed on the body""s outer surface such that a complementary threaded top can be fit thereon; at least one recess disposed in an outer surface of the body and axially distant from the threaded groove. The recess is adapted to receive an O-ring to facilitate better sealing as well as easier, safer removal. At least one aperture is disposed therein to receive a fluid injection line. The capping mechanism itself may include at least one elastic vent member with at least one slit and at least one channel disposed therein; and at least one membrane plate with at least one recess and at least one channel disposed therein, where the recess is in substantially axial alignment with the slit. Slits placed in the compliant members can respond to pressure differentials between the inside and outside of the container, which then permits the insertion and withdrawal of fluid. In the alternative, the capping mechanism may include: a plurality of passages; at least one venturi; a plurality of generally spherical stoppers disposed within a chamber in the body such that they are seatably responsive to a pressure differential in the fluid transfer line that extends between the container and the fluid transport conduit, such that, upon exposure to a pressure differential, the generally spherical stoppers change their seating arrangement against the aperture. Another desirable attribute of the present invention is its incorporation of fluid containment devices that permit relatively xe2x80x9chandsfreexe2x80x9d fluid dispensing system operation of handling acids, solvents and dispensing liquid neutralizer. For example, the inventors discovered that when the mixing process involves hazardous substances, such as acids and related etchants, exposure of the vapors and liquids to personnel and sensitive equipment could be minimized through the use of an appropriate capping mechanism. The features of the capping mechanism permit the uninhibited access of fluid to and from the fluid container while simultaneously minimizing the chance of liquid spillage or inadvertent venting of corrosive or noxious vapors. With the inclusion of features such as this, the present invention greatly increases the efficiency of dispensing and neutralization processes by integrating improved safety features into the dispensing system""s inherently simple design. As another option, a filter is disposed in the fluid injection lines to provide fluid damping. Additional options to the flow detection system include specific detector features. For example, the detector can be either an ultrasonic or optical detector, where more specifically, in embodiments using the optical detector, it can be an IR detector. Another option is the inclusion of a neutralizer with integral dye indicator into the fluid dispensing system. The neutralizer comprises a base in liquid solution mixed with a dye indicator. Upon addition to an acidic solution, the pH changes. When the pH range of 6 to 8 is achieved, the solution undergoes an abrupt color change. One example of such a neutralizer is triethanolamine, although other solutions, including sodium hydroxide, can be used. Another option includes an enclosure to house one or more of the various components of the fluid dispensing system such that they are disposed within the enclosure. Preferably, the enclosure contains the pump and valve assembly, and is sized to conveniently fit in a fume hood, or on top of a table designed to house fluid reagents, thus providing a compact, autonomous container for the fluid dispensing system.
In accordance with another embodiment of the present invention, a cam assembly is disclosed. The apparatus comprises a shaft, a rotational member, a cam, and a cam driver. The shaft and rotational member each include an axis of rotation along their respective length. The cam moves in at least two degrees of freedom, where the first is preferably a translational movement operatively responsive to its threaded relationship with the turning shaft, and the second is preferably a rotational movement operatively responsive to the interaction between complementary mating cam and rotational member surfaces. Furthermore, each cam degree of freedom movement is independently responsive to shaft and rotational member motion, caused in turn by the cam driver coupled to the shaft and rotational members. In the present context, xe2x80x9cindependently responsivexe2x80x9d means that even though the cam is coupled to both the shaft and the rotational member, it does not require the simultaneous movement of both to perform its intended function. To take up as little space as possible, that shaft can be disposed concentrically inside a hollow portion of the rotational member, and the cam can be disposed on an outer surface of the rotational member so that the axes of rotation of the shaft, cam and rotational member are coaxial. This space-saving feature is highly desirable in volume-limited applications, such as when working with hazardous substances, where the entire assembly might need to be located in a fume hood or similar device. Moreover, the cam driver need not be a single motor, but instead can comprise a first motor for imparting translational movement to the shaft, and a second motor for imparting rotational movement to the rotational member.
In accordance with another embodiment of the present invention, a flow control apparatus for porting fluids is disclosed. The apparatus comprises a housing and a plurality of valves, in addition to the cam assembly described in the previous embodiment. The housing supports the plurality of valves, as well as the shaft, cam and rotational member. Each one of the valves include a valve actuator, that, on one end, is connected to the valve such that movement of the actuator opens or closes the valve. The other end of the actuator engages the eccentric portion of the cam such that rotational changes in the cam produce changes in the actuator""s position. In addition, a flow detection system with at least one ultrasonic or optical sensor may be included, and, in the case of an optical detector, operable in either the IR or visible band. This flow detection system can be integrated into a microprocessor-based controller to ensure accurate and repeatable quantities of mixing fluids are being drawn into the mixing region of the pump from their containers. As with the aforementioned fluid dispensing system, this apparatus is especially well-suited to the use of acids, solvents and acid neutralizers.
In accordance with yet another embodiment of the present invention, a fluid dispensing system is disclosed. The fluid dispensing system comprises, a pump, a fluid transport conduit, a valve assembly and a flow detection system, and a dispensing unit in fluid communication with the valve assembly to accept fluid from the fluid transport conduit. The fluid transport conduit provides a containment path through which the injectant fluids can be circulated. The flow detection system (similar to the previously described fluid dispensing system) is in fluid communication with the fluid transport conduit, as is the valve assembly. The valve assembly contains a plurality of valves, each of which includes a valve actuator. While the valves are designed to be either open or closed, they could optionally be coupled to a feedback-based controller to provide flow rate control. The valve assembly itself comprises a housing, shaft, rotational member, cam and cam driver similar to that of the previous embodiment. Optionally, the fluid dispensing system further comprises at least one container for supplying the injectant, where the container is in fluid communication with the valve assembly and fluid transport conduit. The aperture of the container may have a capping mechanism similar to that described in conjunction with the previous fluid dispensing system embodiment. As with the prior fluid dispensing system embodiment, an enclosure can be included to house one or more of the individual components within the fluid dispensing system. Additionally, the fluid dispensing system includes safety and convenience features, such as a dispensing unit including a dispensing nozzle to facilitate the introduction of fluid in the fluid transport conduit into a receiving container (such as a beaker), a mixing device (such as a magnetic stirrer) to improve mixing of dispensed fluid in the receiving container, a door disposed on the enclosure to prevent fluid spillage from escaping, an interlock that prevents the fluid dispensing system from operating until the door is closed, a drain disposed within the dispensing unit to collect any fluid spillage inside the dispensing unit, a pressure relief valve to protect the fluid transport conduit from becoming overpressurized, and a waste receptacle attached to the drain and pressure relief valve. Optionally, the fluid dispensing system can accommodate various pusher fluids in a fashion similar to that of the previous embodiment fluid dispensing system. Also as with the previous embodiment fluid dispensing system, a neutralizer with integral dye indicator can be added to facilitate efficient neutralization of the dispensed fluids, which can include, among others, acids, solvents and acid neutralizers.
In accordance with still another embodiment of the present invention, a method for controlling the amount of fluid flowing through at least one of a plurality of valves is disclosed. The method comprises the steps of placing at least one fluid container in operative communication with at least one valve, arranging a valve actuator to be in mechanical communication with the valve, mounting a cam to both a shaft and a rotational member such that the cam is operatively responsive to movements in the shaft and rotational members, placing a cam driver to provide translational and rotational movement to the cam through the shaft and rotational member, and controlling the opening or closing of the valve in response to a predetermined process condition. This last step is accomplished by receiving an input from a control mechanism, sending a control signal from the control mechanism to the cam driver, translating the cam until it is aligned with the valve actuator, then rotating the cam to force engagement between it and the valve actuator to open the valve until a desired amount of fluid is injected into the fluid transport conduit. Optionally, the method is accomplished with a device that has the shaft axis of rotation coaxial with the rotational member axis of rotation, and where the control mechanism comprises a microprocessor-based controller. The method may also include installing a flow detection system, whereby air pockets or bubbles injected into either the fluid transport conduit or the fluid injection lines can be sensed, then correlating the sensed value against a predetermined fluid volume to be dispensed, then calculating a flow adjustment signal to send to the cam driver to adjust the valve to remain open for an additional period to ensure adequate quantities of fluid are dispensed. Other features that may be incorporated include an aperture in the fluid container with a capping mechanism such that when the fluid is flowing neither to nor from the container, the capping mechanism prevents the fluid from escaping from the container, as well as to facilitate the flow to or from the container during such periods that fluid transport is necessary. Such capping mechanisms having already been described herein.
In accordance with still another embodiment of the present invention, a method for preparing metallurgical etchants is disclosed. The steps of this method include: placing at least one fluid container with a fluid to be dispensed disposed therein in operative communication with at least one valve; arranging a valve actuator to be in mechanical communication with the valve; placing a fluid injection line in fluid communication with the valve such that the fluid injection line is also in operative communication with the fluid container; placing a fluid transport conduit in fluid communication with the fluid injection line; placing at least one pump for metering precise quantities of the fluid to be dispensed in fluid communication with the fluid transport conduit, thereby establishing fluid communication between the pump and the fluid container; selectively introducing a pusher fluid into the fluid transport conduit to force the flow of the fluid to be dispensed through the fluid transport conduit; monitoring the flow of the fluid to be dispensed through the fluid injection line with a flow detection system; controlling the opening or closing of the valve in response to a predetermined process condition by receiving an input from the controller, and sending a control signal from the controller to the valve actuator, thereby forcing engagement between the valve actuator and the valve to an extent dictated by the control signal such that the valve adjusts a flow of the fluid to be dispensed; and operating the pump to move a predetermined amount of the fluid to be dispensed from the fluid container, through the valve, fluid injection line, fluid transport conduit, and into a dispensing unit in fluid communication with the fluid transport conduit so as to accept fluid therefrom. The flow detection system itself comprises at least one detector placed in sensor communication with the fluid injection line and a controller in electrical communication with the detector, valve and pump such that upon detection and comparison of a flow variation, the controller sends signals to at least the pump or valve to control the flow of the fluid to be dispensed. Optionally, the fluid to be dispensed by the method is an acid, solvent or acid neutralizer. The method may further include a step to neutralize the etchant after use by dispensing an acid neutralizer with an integral dye indicator contained therein to indicate when a desired pH level is attained. This step could obviate the need to iteratively adjust the pH of the spent etchant.
In accordance with still another embodiment of the present invention, a method for preparing metallurgical etchants is disclosed, comprising the steps of: placing at least one fluid container with a fluid disposed therein in operative communication with at least one valve of a plurality of valves; arranging a valve actuator to be in mechanical communication with the valve; mounting a cam to both a shaft with an axis of rotation along its length and a rotational member with an axis of rotation along its length such that the cam is independently responsive to rotation of the shaft and rotational member; placing a cam driver for translating and rotating the cam relative to the valve in operative communication with both the shaft and rotational member; and controlling the opening or closing of the valve in response to a predetermined process condition. The step of controlling includes the following: receiving an input from a control mechanism; sending a control signal from the control mechanism to the cam driver; translating the cam until the cam is aligned with the valve actuator; and rotating the cam to force engagement between it and the valve actuator to an extent dictated by the control signal such that the valve actuator forces the valve to adjust a flow of the fluid therethrough. Optionally, the fluid to be dispensed is an acid, solvent or acid neutralizer, where the neutralizer can include an integral dye indicator.
Other features and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.